Private Browsing Mode Is Not Private

All web browsers now offer ‘private’ or incognito browsing modes. However, while the private browsing mode may stop other people using your computer accidentally stumbling across your browser history, there are no match for someone more inquisitive.

Private mode stops your browser software (ie. Firefox, Chrome etc) recording your browsing, but they do not stop your activities being recorded by other software:-

It is easy for Spyware, malware, keylogger etc. software to install itself on your computer without you being aware it is there.  This software can record your browsing. For example, keylogger software records every key that you type.

Private browsing only attempts to control what your browser saves on your computer. It does not control information your internet service provider (ISP) saves about you on their servers.
Your history, such as google searches, will still be recorded on the websites you have logged into. For example, if you are logged into your Google, You Tube or Facebook accounts then neither using private browsing or deleting your browser history will not remove your online search history.
You can still download files into your Downloads folder on your windows computer while in private browsing mode.

If you are using Internet Explorer then your browsing history is still stored in a multitude of ‘index.dat’ files scattered across your computer. To make things worse, these are not deleted when you clear your browser history.  Find out how to clear the index.dat files in Internet Explorer.
Any plugins or add-ons software installed in your browser (sometimes without your knowledge) can still record information about your browsing history even when you are in private mode.

Therefore, while  ’private browsing’ is technically an accurate term in the sense that the browser software itself is private, it is misleading because it stops people considering the other (above mentioned) software that may be recording their searches and leads them to believe that it is their browsing that is private. You may also like to read about why clearing or deleting your history is not enough.


References
Aggarwal, G., Bursztein, E., & Jackson, C. (2010). An analysis of private browsing modes in modern browsers. [This Stanford university research is the key paper that subsequent research has sprung from. Summary of the Stanford paper.]

Ruiz-Martínez, A. (2012). A survey on solutions and main free tools for privacy enhancing Web communications. Journal of Network and Computer Applications
Volume 35, Issue 5, September 2012, Pages 1473–1492.

Komando, K. (2013). How safe if private browsing?

Weinberg, Z. Chen, E., Jayaraman, P. & Jackson, C. (2011).  I Still Know What You Visited Last Summer: Leaking Browsing History via User Interaction and Side Channel Attacks,” Security and Privacy (SP), 2011 IEEE Symposium on , vol., no., pp.147,161.